Known hydraulic control apparatuses for automatic transmissions have been disclosed, which directly controls hydraulic pressure from a hydraulic power source in accordance with an electric signal to control hydraulic pressure supplied to a engagement element in order to obtain smooth and high-responsive feeling when changing shifts.
According to a known hydraulic control apparatus for an automatic transmission described in U.S. Pat. No. 5,577,584 (FIG. 1), pressure gain is changed by applying the pressurized oil to control lands (26, 28) which have the difference in dimensions by changing controlled pressure supplied from a regulator valve (14) to a engagement element (10) by a shift valve (16).
According to a known hydraulic control apparatus for an automatic transmission described in U.S. Pat. No. 5,911,244 (FIG. 1), by changing controlled pressure supplied from a regulator valve (14) to a engagement element (54) by means of a control valve (16), pressurized oil applied to control lands (36, 38) which have the difference in dimensions via an orifice (66) is supplied from a passage (56) to a passage (58) to change pressure gain by applying the pressurized oil to control lands (36, 38) which have the difference in dimensions.
According to a known hydraulic control apparatus for an automatic transmission described in JPH06-33953 (FIG. 1), pressure gain is changed by applying controlled pressure to a control land (8b) of a fastening pressure control valve (7) and a plug (9) by a switching valve (11) which have the difference in dimensions.
According to the known hydraulic control apparatuses for the automatic transmissions, by changing a dimension, to which hydraulic pressure applies, of a chamber into which the pressure to change the gain is supplied, characteristics of outputted pressure of a control valve can be changed.
Notwithstanding, it is necessary to replace a spool and a valve body simultaneously when changing characteristics of outputted pressure of a control valve by changing a dimension, to which the hydraulic pressure applies, of a chamber into which the pressure to change the gain is supplied. This brings a significant change in practice in order to conform to required characteristics. Accordingly, there is a drawback practically in order to respond to varieties of characteristics of an outputted pressure of a control valve.
Generally, a shift is changed at a lower gain side at which controllability is high, and the pressure gain is switched to a higher gain side after the completion of the shift change. However, with the construction of the known hydraulic control apparatus for the automatic transmission described in U.S. Pat. No. 5,911,244, because the size of a plug valve of a regulator valve is large, when switching the pressure gain from the lower gain to the higher gain, there are drawbacks that a volume change of a TRIM is significant, a controlled pressure declines, and a torque amount applied to a engagement element declines.
A need thus exists for a hydraulic control apparatus for an automatic transmission, which conforms to varieties of characteristics of an outputted pressure of a control valve by a slight change.